The invention relates to tool wear rate and tool-failure monitoring. The performance of the cutting tool in machine tools and manufacturing processes is most critical to productivity, as stated in Iron Age, July 27, 1981 "Does Adaptive Control Still Promise Improved Productivity" by Raymond J. Larsen, pp. 57-68. In particular, a reliable tool breakage detection system is essential to avoid loss of cutting tolerances, overload and catastrophic failure. Attempts have been made to follow the tool deterioration process, either by direct viewing techniques, by reference to models, or even by material exploration for possible internal flaws.
Another approach to the problem is found in "Investigation of Adaptive Exponential Smoothing Algorithms in Monitoring Tool Wear" by W. R. DeVries, J. F. Raski and J. C. Mazur, a paper presented at North American Metalworking Research Conf. IX, on pp. 523-527.
There, an exponential smoothing algorithm is used to detect any significant deviations from an established trend in the cutting force as it is continuously sensed, e.g. as an indication of changes in the wear pattern as they develop. With such an approach, predictions are in fact made which are based on past measurements.
Another prior art technique disclosed in copending application Ser. No. 100,674, now U.S. Pat. No. 4,351,029 on Dec. 5, 1979, by Maxey et al. relies on net power measurement and derives the integration thereof of a function of time to obtain by reference to experience with a similar tool, the life expectancy of a particular tool, thereby to avoid the critical event once the end of such life expectancy is about to be reached.
In contrast to any of the prior art approaches, the present invention provides (1) for knowing at any given time, for any given tool, under any cutting condition, where the tool is operating, between zero and 100% wear, under its normal life time conditions and (2) for instantaneously detecting, whether such wear rate conditions have been reached which require an immediate shutdown, tool maintenance of changing of tool, thereby to prevent catastrophic tool failure.
The invention also provides for overall monitoring of tool wear and/or tool failure in hydraulically, electromechanically controlled or a computerized installation involving multi-tool and multi-process operation with individual, or centralized control and supervision.